System and method for over-the-air antenna calibration

ABSTRACT

An antenna calibration system for a phased array antenna in accordance with one embodiment of the present disclosure generally includes: a beamformer lattice including at least first and second beamformers, each corresponding to a subset of antenna cells, and each including a calibration section for comparing a reference signal to a non-reference signal; and a calibration antenna within the subset of antenna cells corresponding with the first beamformer, wherein the calibration antenna is configured to deliver a first reference signal (mTx) from the first beamformer to be received by a first operating antenna for comparison with a first non-reference signal (Rx) in the first beamformer or in the second beamfomer, and/or wherein the calibration antenna is configured to deliver a second non-reference signal (Tx) from a second operating antenna for comparison with a second reference signal (mRx) in the first beamformer or in the second beamformer.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.63/048,174, filed Jul. 5, 2020, and U.S. Provisional Application No.63/063,209, filed Aug. 7, 2020, the disclosures of which are herebyexpressly incorporated by reference in the present application.

TECHNICAL FIELD

The present disclosure pertains to antenna apparatuses for satellitecommunication systems and calibration architectures for antenna arrays.

BACKGROUND

Satellite communication systems generally involve Earth-based antennasin communication with a constellation of satellites in orbit.Earth-based antennas are, of consequence, exposed to weather and otherenvironmental conditions. Therefore, described herein are antennaapparatuses and their housing assemblies designed with sufficientdurability to protect internal antenna components while enabling radiofrequency communications with a satellite communication system, such asa constellation of satellites.

SUMMARY

The present disclosure pertains to antenna apparatuses for satellitecommunication systems and calibration architectures for antenna arrays.

In accordance with one embodiment of the present disclosure, an antennacalibration system for a phased array antenna is provided. The antennacalibration system generally includes: a beamformer lattice including atleast first and second beamformers, wherein each of the first and secondbeamformers corresponds to a subset of antenna cells of a plurality ofantenna cells, and wherein each of the first and second beamformersincludes a calibration section for comparing a reference signal to anon-reference signal; and a calibration antenna within the subset ofantenna cells corresponding with the first beamformer, wherein thecalibration antenna is configured to deliver a first reference signal(mTx) from the first beamformer to be received by a first operatingantenna for comparison with a first non-reference signal (Rx) in thefirst beamformer or in the second beamfomer, and/or wherein thecalibration antenna is configured to deliver a second non-referencesignal (Tx) from a second operating antenna for comparison with a secondreference signal (mRx) in the first beamformer or in the secondbeamformer.

In accordance with another embodiment of the present disclosure, amethod for antenna calibration is provided. The method generallyincludes: obtaining a beamformer lattice including at least first andsecond beamformers, wherein each of the first and second beamformerscorresponds to a subset of antenna cells of a plurality of antennacells, and wherein each of the first and second beamformers includes acalibration section for comparing a reference signal to a non-referencesignal; and using a calibration antenna within the subset of antennacells corresponding with the first beamformer to calibrate the subset ofantenna cells, wherein the calibration antenna is configured to delivera first reference signal (mTx) from the first beamformer to be receivedby a first operating antenna for comparison with a first non-referencesignal (Rx) in the first beamformer or in the second beamfomer, and/orwherein the calibration antenna is configured to deliver a secondnon-reference signal (Tx) from a second operating antenna for comparisonwith a second reference signal (mRx) in the first beamformer or in thesecond beamformer.

In accordance with another embodiment of the present disclosure, anantenna calibration system for a phased array antenna if provided. Theantenna calibration system generally includes: a beamformer latticeincluding at least a first beamformer, wherein the first beamformercorresponds to a plurality of antenna cells, and wherein the firstbeamformer includes a calibration section for comparing a referencesignal to a non-reference signal; and a calibration antenna within theplurality of antenna cells corresponding with the first beamformer,wherein the calibration antenna is configured to deliver a firstreference signal (mTx) from the first beamformer to be received by afirst operating antenna for comparison with a first non-reference signal(Rx) in the first beamformer and/or wherein the calibration antenna isconfigured to deliver a second non-reference signal (Tx) from a secondoperating antenna for comparison with a second reference signal (mRx) inthe first beamformer.

In accordance with another embodiment of the present disclosure, amethod for antenna calibration is provided. The method generallyincludes: obtaining a beamformer lattice including at least a firstbeamformer, wherein the first beamformer corresponds to a plurality ofantenna cells, and wherein the first beamformer includes a calibrationsection for comparing a reference signal to a non-reference signal; andusing a calibration antenna to calibrate the plurality of antenna cellscorresponding with the first beamformer, wherein the calibration antennais configured to deliver a first reference signal (mTx) from the firstbeamformer to be received by a first operating antenna for comparisonwith a first non-reference signal (Rx) in the first beamformer and/orwherein the calibration antenna is configured to deliver a secondnon-reference signal (Tx) from a second operating antenna for comparisonwith a second reference signal (mRx) in the first beamformer.

In any of the embodiments described herein, the first reference signalmay be delivered from a calibration section (mTx) of the firstbeamformer.

In any of the embodiments described herein, the second non-referencesignal (Tx) may be received in a calibration section (mRx) of the firstbeamformer.

In any of the embodiments described herein, the first reference signalmay be delivered from an RFIO of the first beamformer.

In any of the embodiments described herein, the second non-referencesignal may be received in an RFIO of the first beamformer.

In any of the embodiments described herein, the calibration antenna maybe configured to deliver a first reference (mTx) signal from the firstbeamformer to be received by a first operating antenna for comparisonwith a first received non-reference (Rx) signal in the first beamformerand a second operating antenna for comparison with a second receivednon-reference signal (Rx) in the second beamfomer.

In any of the embodiments described herein, the calibration antenna maybe configured to receive a first non-reference (Tx) signal from a firstoperating antenna associated with the first beamformer and a secondnon-reference (Tx) signal from a second operating antenna associatedwith the second beamformer for comparison with a first reference signal(mRx) in the first beamformer.

In any of the embodiments described herein, the calibration antenna maybe configured to operate partially as a calibration antenna andpartially as an operating antenna.

In any of the embodiments described herein, the first and secondoperating antennas may be configured for sending signals, receivingsignals, or both.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a not-to-scale diagram illustrating a simple example ofcommunication in a satellite communication system in accordance withembodiments of the present disclosure.

FIGS. 2A and 2B are isometric top and bottom views depicting anexemplary antenna apparatus according to one embodiment of the presentdisclosure.

FIG. 3A is an isometric exploded view depicting an exemplary antennaapparatus including the housing and the antenna stack assembly accordingto one embodiment of the present disclosure.

FIG. 3B is a cross-sectional view of an antenna stack assembly of anantenna apparatus in accordance with some embodiments of the presentdisclosure.

FIG. 4A is an exemplary illustration showing a simplified block diagramof an RF path for an antenna assembly including a dual-linear polarizedantenna, 3-dB 90-deg hybrid, TX/RX front-end-module (FEM) chip, anddigital beam former (DBF) chip connected with bidirectional RF I/Olines, in accordance with some embodiments of the present disclosure.

FIG. 4B is an example illustration of a top view of an antenna latticein accordance with some embodiments of the present disclosure.

FIG. 4C is an exemplary illustration showing a beamformer latticeassociated with an antenna lattice, in accordance with some embodimentof the present disclosure.

FIG. 5A is a close-up top view of the radome spacer of an antenna stackassembly in accordance with some embodiments of the present disclosureshowing the upper patches of antenna elements in apertures of the radomespacer.

FIG. 5B is a close-up top view of the radome spacer of an antenna stackassembly in accordance with some embodiments of the present disclosureshowing the upper patches of antenna elements in apertures of the radomespacer.

FIG. 5C is a top view of the upper patch antenna layer an antenna stackassembly in accordance with some embodiments of the present disclosure.

FIG. 5D is a top view of the antenna spacer an antenna stack assembly inaccordance with some embodiments of the present disclosure.

FIG. 5E is a top view of the lower patch antenna layer an antenna stackassembly in accordance with some embodiments of the present disclosure.

FIGS. 6A-6D are various close-up isometric, top, and cross-sectionalviews of an antenna stack assembly in accordance with some embodimentsof the present disclosure.

FIG. 6E is a close up cross-sectional view of an antenna apparatusincluding a twelve-layer PCB assembly stack-up and DBF, FEM and antennacavity routing inside that PCB assembly layers in accordance with someembodiments of the present disclosure.

FIGS. 7A-7C are exemplary views of circuitry components in a pluralityof layers of a PCB assembly an antenna stack assembly in accordance withsome embodiments of the present disclosure.

FIGS. 8A-8E are exemplary views showing circuitry components in aplurality of layers of a PCB assembly an antenna stack assembly inaccordance with some embodiments of the present disclosure. FIG. 8C-8Eare exemplary views showing a coupler design placed between the 90-deghybrid and the FEM to be used to couple the calibration/measurementRX/TX ports to the functional paths.

FIGS. 9A-9F are exemplary schematics showing circuitry and signal pathsfor a beamformer calibration system in accordance with some embodimentsof the present disclosure.

DETAILED DESCRIPTION

Various embodiments of the disclosure are discussed in detail below.While the concepts of the present disclosure are susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and will be describedherein in detail. It should be understood, however, that there is nointent to limit the concepts of the present disclosure to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives consistent with the presentdisclosure and the appended claims.

In the drawings, some structural or method features may be shown inspecific arrangements and/or orderings. However, it should beappreciated that such specific arrangements and/or orderings may not berequired. Rather, in some embodiments, such features may be arranged ina different manner and/or order than shown in the illustrative figures.Additionally, the inclusion of a structural or method feature in aparticular figure is not meant to imply that such feature is required inall embodiments and, in some embodiments, it may not be included or maybe combined with other features.

References in the specification to “one embodiment,” “an embodiment,”“an illustrative embodiment,” etc., indicate that the embodimentdescribed may include a particular feature, structure, orcharacteristic, but every embodiment may or may not necessarily includethat particular feature, structure, or characteristic. Moreover, suchphrases are not necessarily referring to the same embodiment. Further,when a particular feature, structure, or characteristic is described inconnection with an embodiment, it is submitted that it is within theknowledge of one skilled in the art to affect such feature, structure,or characteristic in connection with other embodiments whether or notexplicitly described. Language such as “top”, “bottom”, “upper”,“lower”, “vertical”, “horizontal”, “lateral”, in the present disclosureis meant to provide orientation for the reader with reference to thedrawings and is not intended to be the required orientation of thecomponents or to impart orientation limitations into the claims.

The phrase “coupled to” refers to any component that is physicallyconnected to another component either directly or indirectly, and/or anycomponent that is in communication with another component (e.g.,connected to the other component over a wired or wireless connection,and/or other suitable communication interface) either directly orindirectly.

Embodiments of the present disclosure are directed to antennaapparatuses including antenna systems designed for sending and/orreceiving radio frequency signals and calibration architecture for suchantenna apparatuses.

The antenna systems of the present disclosure may be employed incommunication systems providing high-bandwidth, low-latency networkcommunication via a constellation of satellites. Such constellation ofsatellites may be in a non-geosynchronous Earth orbit (GEO), such as alow Earth orbit (LEO). FIG. 1 illustrates a not-to-scale embodiment ofan antenna and satellite communication system 100 in which embodimentsof the present disclosure may be implemented. As shown in FIG. 1, anEarth-based endpoint or user terminal 102 is installed at a locationdirectly or indirectly on the Earth's surface such as house or other abuilding, tower, a vehicle, or another location where it is desired toobtain communication access via a network of satellites.

A communication path may be established between the endpoint terminal102 and a satellite 104. In the illustrated embodiment, the firstsatellite 104, in turn, establishes a communication path with a gatewayterminal 106. In another embodiment, the satellite 104 may establish acommunication path with another satellite prior to communication with agateway terminal 106. The gateway terminal 106 may be physicallyconnected via fiber optic, Ethernet, or another physical connection to aground network 108. The ground network 108 may be any type of network,including the Internet. While one satellite 104 is illustrated,communication may be with and between a constellation of satellites.

The endpoint or user terminal 102 may include an antenna system disposedin an antenna apparatus 200, for example, as illustrated in FIGS. 2A and2B, designed for sending and/or receiving radio frequency signals toand/or from a satellite or a constellation of satellites. The antennasystem, may include an antenna aperture 208 defining an area fortransmitting and receiving signals, such as a phased array antennasystem or another antenna system.

FIG. 2B illustrates a perspective view of an underside of the antennaapparatus 200. As shown, the antenna apparatus 200 may include a lowerenclosure 204 that couples to the radome portion 206 to define thehousing 202. In the illustrated embodiment, the mounting system 210includes a leg 216 and a base 218. The base 218 may be securable to asurface S and configured to receive a bottom portion of the leg 216. Atilting mechanism 220 (details not shown) disposed within the lowerenclosure 204 permits a degree of tilting to point the face of theradome portion 206 at a variety of angles for optimized communicationand for rain and snow run-off.

Referring to FIG. 3A, an antenna stack assembly 300 includes a pluralityof antenna components, which may include a printed circuit board (PCB)assembly 342 configured to couple to other electrical components thatare disposed within the housing assembly 202 (made up of lower enclosure204 and radome assembly 206). In the illustrated embodiment, the antennastack assembly 300 includes a phased array antenna assembly made up froma plurality of individual antenna elements configured in an array. Thecomponents of the phased array antenna assembly 334 may be mechanicallyand electrically supported by the printed circuit board (PCB) assembly342.

In the illustrated embodiment of FIGS. 3A and 3B, the layers in theantenna stack assembly 300 layup include a radome assembly 206(including radome 305 and radome spacer 310), a phased array patchantenna assembly 334 (including upper patch layer 330, lower patch layer332, and antenna spacer 335 in between), a dielectric layer 340, and aprinted circuit board (PCB) assembly 342, as will be described ingreater detail below. As seen in FIG. 3B, the layers may includeoptional adhesive coupling 325 between adjacent layers.

Phased Array Antenna System

FIGS. 4A-4C are schematic illustrations of the electronic system of aphased array antenna system 400 in accordance with embodiments of thepresent disclosure. The phased array antenna system 400 is designed andconfigured to transmit or receive a combined beam composed of signals(also referred to as electromagnetic signals, wavefronts, or the like)in a preferred direction from or to an antenna aperture 402 (see FIG.4C). Accordingly, the plurality of antenna elements simulate a largedirectional antenna. An advantage of the phased array antenna is itsability to transmit and/or receive signals in a preferred direction(i.e., the antenna's beamforming ability) without physicallyrepositioning or reorienting the system.

In accordance with one embodiment of the present disclosure, a phasedarray antenna system may be configured to transmit and/or receive radiofrequency (RF) signals. The antenna system includes a phased arrayantenna including a plurality of antenna elements 413 defining antennaaperture 402, for example, antenna elements 413 distributed in one ormore rows and/or columns (see FIG. 4C) and a plurality of phase shifters(not shown) configured for generating phase offsets between the antennaelements 413. As a non-limiting example, a two-dimensional phased arrayantenna may be capable of electronically steering in two directions.

Referring to FIGS. 4A-4C, the illustrated phased array antenna system400 includes an antenna lattice 412 including a plurality of antennaelements 413, 414 and a beamformer lattice 406 including one or moredigital beamformer (DBF) chips 407, 408 (which may be referred to hereinas digital beamformers, DBFs, or DBF chips herein) for receiving signalsfrom a modem 410 in the transmit (Tx) direction and sending signals tothe modem 410 in the receive (Rx) direction. The antenna lattice 412 isconfigured to transmit or receive a combined beam of radio frequencysignals having a radiation pattern from or to the antenna aperture 402(see FIG. 4C). In the illustrated embodiment of FIGS. 4B and 4C, theantenna lattice 412 includes a plurality of antenna elements 413 in afirst set or grouping.

The plurality antenna elements 413 in the antenna lattice 412 areconfigured for transmitting signals and/or for receiving signals.Referring to FIG. 4B, the antenna aperture 402 of the phased arrayantenna system 400 is the area through which the power is radiated orreceived. A phased array antenna synthesizes a specified electric field(phase and amplitude) across an aperture 402. As described in greaterdetail below, the antenna lattice 412 defining the antenna aperture 402may include the plurality of antenna elements 413 arranged in aparticular configuration that is supported physically and electronicallyby a printed circuit board (PCB) (see FIG. 6E).

Referring to FIG. 4A, a corresponding plurality of front end module(FEM) chips 415 (which may be referred to as front ends (Fes), front endmodules (FEMs) or FEM chips herein) are coupled to the plurality ofantenna elements 413. The FEM chips may include low noise amplifiers(LNAs) 424 in the receiving direction Rx or power amplifiers (PAs) 423in the transmitting direction Tx. Although shown in the illustratedembodiment of FIG. 4A as a separate chip from the DBF chip 407, itshould be appreciated that some or all of the components in the FEMchips 415 may be incorporated into the associated DBF chip 407.

The beamformer lattice 406 includes a plurality of digital beamformers(DBFs) 407, 408 (see FIG. 4C) including a plurality of phase shifters(not shown). In the receiving direction (Rx), the beamformer function isto delay the signals arriving from each antenna element such that thesignals all arrive to the combining network at the same time. In thetransmitting direction (Tx), the beamformer function is to delay thesignal sent to each antenna element such that all signals arrive at thetarget location at the same time. This delay can be accomplished byusing “true time delay” or a phase shift at a specific frequency.

In the illustrated embodiment of FIG. 4C, each Tx/Rx DBF 407, 408 iscapable of processing transmit and receive signals. However, in otherembodiments, a DBF chip associated with each group of antenna elementsmay be configured for either transmit or receive.

Referring to FIG. 4C, the plurality of DBF chips in the beamformerlattice 406 may include an L number of DBF chips. For example, DBF chip407 comprises the first DBF chip (i=1, where i=1 to L), and so forth, toDBF 408 comprising the Lth DBF chip (i=L) of the plurality of DBF chips406. Each DBF chip of the plurality of DBF chips 406 electricallycouples with a group of respective M number of antenna elements of theplurality of antenna elements. In the illustrated example, DBF 407electrically couples with M antenna elements 413 and DBF 408electrically couples with M antenna elements 414. In the illustratedembodiment, the plurality of DBF chips 406 are electrically coupled toeach other in a daisy chain arrangement. However, other couplingarrangements are within the scope of the present disclosure.

In some embodiments, each DBF chip of the plurality of DBF chips 406comprises an IC chip or IC chip package including a plurality of pins,in which at least a first subset of the plurality of pins is configuredto communicate signals with its electrically coupled DBF chip(s) (if ina daisy chain configuration) and/or modem 410 in the case of DBF 407, asecond subset of the plurality of pins is configured to transmit/receivesignals with M antenna elements, and a third subset of the plurality ofpins is configured to receive a signal from a reference clock 416 and/ora local oscillator (not shown). The plurality of DBF chips 406 may alsobe referred to as transmit/receive (Tx/Rx) DBF chips, Tx/Rx chips,transceivers, DBF transceivers, and/or the like. As described above, theDBF chips may be configured for Rx communication, Tx communication, orboth. In some embodiments, each DBF chip of the plurality of DBF chips406 may be configured to operate in half duplex mode, in which it iscapable of receiving or transmitting RF signals/waveforms but not bothsimultaneously.

Referring to FIG. 4B, the antenna aperture 402 may be grouped intosubsets of antenna elements 404 a and 404 b. Each subset 404 a, 404 b ofthe plurality of antenna elements can comprise the M antenna elements413, 414, which may be associated with specific DBF chips 407, 408. Theremaining antenna elements 415 of the plurality of antenna elements maybe similarly associated with other DBF chips (not shown) in theplurality of DBF chips 406.

FIG. 4A is an example illustration showing circuitry or electricalcomponents included in and/or associated with a single DBF 407 inaccordance with some embodiments of the present disclosure. The contentsof each of the DBF chips 406 are similar to that discussed herein forDBF 407.

In some embodiments, DBF chip 407 includes, among other components, atransmit section 421, a receive section 422, and a calibration sectionincluding a transmit calibration (mTx) 431 and a receive calibration(mRx) 432. DBF 407 is configured to generate RF signals (based on dataprovided by modem 410) to be transmitted by antenna elements 413, decodeRF signals received by antenna elements 413 to provide to modem 410,calibrate the receive section 422 (also referred to as a receiver orreceiver section) using the transmit calibration (mTx) 431 andcalibration antenna element 413 a, and calibrate the transmit section421 (also referred to as a transmitter or transmitter section) using thereceive calibration (mRx) 432 and calibration antenna element 413 a.

Transmit and receive calibrations (mTx and mRx) 431 and 432 areselectively electrically coupled to a calibration antenna element 413 a.A calibration antenna element may be an antenna element included in theantenna lattice 412. In some embodiments, a calibration antenna elementis configured for performing calibrations only as acalibration-dedicated antenna element. In other embodiments, acalibration antenna element may be any of the M antenna elements 413 ina subset of antenna elements associated with a DBF 407 and, when notcalibrating, may be used for normal or regular signal communicationlinks. Transmit and receive calibrations (mTx and mRx) 431, 432 areconfigured to facilitate obtaining calibration measurements so as toadapt receive and transmit sections 421, 422, respectively, tocompensate for phase and/or time delay mismatch produced by DBF 407, orother DBF chips in the beamformer lattice 406, PCB traces, associatedantenna elements, and/or associated antenna element circuitry.

In some embodiments, the transmit (Tx) section 421 includes a transmitdigital beamformer (Tx DBF) section 425 and a plurality of Tx RFsections 427 including components. A data signal or stream may beprovided by the modem 410 and comprises the input to the Tx section 421.

Tx RF sections 427 are configured to ready the time delay and phaseencoded digital signals for transmission. The plurality of the transmitRF sections 427 may include M number of transmit RF sections 427, onefor each of the M paths for each antenna element 413. Each transmit RFsection 427 may include other components 433 such as a transmit digitalfront end (Tx DFE), a digital-to-analog converter (DAC), a low passfilter (LPF), a mixer, and a power amplifier (PA).

The amplified RF signal outputted by the PA 423 in the FEM chip 415 isthe input to an antenna element 413. In turn, the antenna element 413radiates the amplified RF signal. Each of the M antenna elements 413 isconfigured to radiate an amplified RF signal generated by a respectivetransmit RF section 427.

In some embodiments, the Rx section 422 includes a plurality of Rx RFsections 428 and a single receive digital beamformer (Rx DBF) section426. Each receive RF section 428 includes components 434 such as a lownoise amplifier (LNA), a mixer, a low pass filter (LPF), ananalog-to-digital converter (ADC), and a receive digital front end (RxDFE). In the FEM chip 415, LNA 424 is configured to perform low noiseamplification of the analog RF signal received at the respective antennaelement 413. A data signal or stream may be provided to the modem 410and comprises the output from the Rx section 421.

Accordingly, DBF 407 is configured to both digitally process a firstdata signal, stream, or beam of a single channel for transmission by afirst plurality of antenna elements; to receive a second data signal,stream, or beam of a single channel using a second plurality of antennaelements; and to digitally recover/reconstitute the original data signalunderlying the received signal. The first and second plurality ofantenna elements may be the same or different from each other.

In some embodiments, phase, time delay, and/or amplitude offset canoccur after an antenna system has been fully calibrated prior to startof normal operations using individual probe measurements,processing-intensive computations, and setting of electrical componentsincluded in the antenna system based on the measurements andcomputations. Such full calibration scheme is referred to as park andmeasurement, park and measurement calibration, and/or the like. Duringnormal operation, park and measurement calibration may not be possible.Thus, calibration techniques for calibrating signals can be used toidentify and appropriately pre-compensate for phase, time delay, and/oramplitude offsets that occur after (or in between) park and measurement.Such offsets comprise deviations from the particular phase, time delay,and amplitude settings associated with electrical components from parkand measurement. At least some of the deviations from park andmeasurement can be due to temperature variations during normaloperation.

Each antenna element of the phased array antenna and its associatedtransmit or receive circuitry undergoes a similar calibration procedureperiodically during operation. Such measurements and calibration basedon the measurements can be performed simultaneously with or independentof normal operation of the phased array antenna (e.g., duringtransmission and receiving of regular or normal signals in the phasedarray antenna). In some embodiments, the calibration processincorporates a waveform generator 441 electrically coupled to each ofthe transmit section 421 and the calibration receive section (mRx) 432and the receive section 422 and the calibration transmit section (mTx)431 for correlation and calibration.

Referring to FIG. 4A, in accordance with one embodiment of the presentdisclosure, a phased array antenna system 400 includes a beamformerlattice 406 including a plurality of DBF chips 407, a front end module(FEM) lattice including a plurality of FEM chips 415, and an antennalattice 412 including a plurality of antenna elements 413, and 90-degreehybrid couplers 462 disposed between each antenna element 413 and eachFEM chip 415.

FIG. 4A shows a schematic block diagram of an exemplary DBF 407 used incontrolling the phase and amplitude of the RF signals going into andcoming from the antenna elements 413 (hence creating the “beam”). TheDBF 407 has functional RF Tx/Rx portions 421 and 422 (including variouscomponents such as Rx and Tx DBF sections 425 and 426, PAs/LNAs, mixers,filters and DAC/ADC, see Tx components 427 and Rx components 428),dedicated RF paths for calibration and measurement (mTx/mRx) 431 and432, and a calibration computing section 443 including a calibrationcode generator 441.

In the illustrated embodiment, coded calibration signals from the CDMAcode generator 443 are shown to be distributable both by RFinput/outputs (RFIO) (see line 451 to Tx DBF section 425) and themTx/mRx ports (see line 453 to mTx section 431), as explained in greaterdetail below with reference to FIGS. 9A-9F.

Pinouts from the DBF 407 for the functional RF input/outputs (RFIO) 457and the calibration ports (mTx, mRx) 465 and 467 are shown in FIG. 4A.In one non-limiting example, the DBF 407 may include 16 functional RFinput/outputs (RFIO) 457, such that each DBF 407 is coupled to 16antenna elements 413. Pinouts from the DBF 407 for a common localoscillator, clock, analog/digital power, high-speed communication, anddigital control are not shown in FIG. 4A.

The front-end modules (FEMs) 415 are chips or circuitry disposed betweenthe beamfomer 407 and the plurality of antenna elements 413. FIG. 4Ashows a front-end module (FEM) 415 and DBF 407 connected to each othervia their RFIO lines 457. As described in FIG. 6E below, in oneembodiment of the present disclosure, the connecting RFIO lines 457 areconnecting traces routed inside a PCB assembly 342. As a non-limitingexample, there are two LNAs 424 and two PAs 423 in each the FEM chip 415for coupling with two antenna elements 413 (the LNAs 424 and PAs 423shown as 2-stage amplifiers with digitally controlled first and secondstages). The FEM chip 415 has common pin for its LNA output and the PAinput from line 457 but separate pins for the PA outputs to line 461 andthe LNA inputs to line 463 (going to the individual antenna elements413).

As a non-limiting example, each antenna element 413 is a dual (linearly)polarized antenna, having two separate ports (one per polarization).Using a 3 dB, 90-deg hybrid combiner/splitter 462, a dual circularlypolarized antenna element is created. Two isolated ports of the 90-deghybrid are connected to the antenna ports via feed lines 456 and 458.The remaining two isolated ports are connected to the RX and TX pins ofthe FEM via lines 461 and 463.

As a non-limiting example, the 16 RFIO of the DBF 407 can control 8 FEMchips 415 (with 2 LNA/PA pairs in each) and 16 dual-port antennaelements 413, together which can be called a DBF “block”. Those numberscan change, depending on the FEM and DBF chip size (and the number ofRFIO lines).

FIG. 4B shows a block diagram for the 2D antenna aperture 402. Each DBFchip 407, 408 is associated with its own set of respective antennaelements 413, 414 (DBF blocks). Each of those DBF blocks has at leastone dual-use antenna element 413 a for calibration. There can bemultiple dual-use calibration antenna elements 413 a, for example, ifthe calibration lines couple to more than one RF path before beingterminated.

Returning to FIG. 4A, the calibration ports (mTx 431 and mRx 432) in theDBF 407 are coupled along regular RF paths 465 and 467 and turn theantenna of that path into a dual-use antenna (capable of regular Tx/Rxfunction and mutual coupling measurements for calibration). See, forexample, line 451 coupling mTx calibration section 431 with Tx DBFsection 425. The routed lines (or traces) 465 and 467 from thecalibration sections (mTx 431 and mRx 432) are configured for tappingalong the RF path using couplers and then terminated with a matchedload. Suitable couplers in accordance with embodiments of the presentdisclosure are described in greater detail below with reference to FIGS.8C-8E.

Instead of coupling to just one antenna, the calibration sections (mTx431 and mRx 432) can be routed (via PCB lines or traces) in a way tocouple to multiple antennas, before being terminated by a matched load.The coupling location can be either between the antenna element 413 andthe FEM 415 or between the FEM 415 and the DBF 407, as described belowwith reference to FIGS. 9A, 9B, 9D, and 9E.

FIG. 4C shows the block diagram of a plurality of DBF blocks 407 and 408and a modem 410 connected to each other via a serial high-speedcommunication link and the central reference (clock 416 and localoscillator) being distributed by a fan-out (H-network) to each DBF chip.Before going into the H-network, the local oscillator and clock signalsare created separately and combined with a diplexer on the PCB assembly(not shown).

The phased array system described in the schematics of FIGS. 4A-4Coperates in a half-duplex mode with the Rx and Tx array sharing the sameantenna aperture 403. During operation, the system might be periodicallyin RX mode, TX mode, or idle mode. To maintain coherent operation ofeach of the RF paths (from antenna to DBF), the system will perform Rxand Tx calibration, which can be performed during any of those modes. InRx mode, the Rx paths in the FEMs and the DBFs will be activated.Likewise in Tx mode, the Tx paths in the FEMs and the DBFs will beactivated. During the Rx and Tx calibration processes, some of the Rxand Tx paths might be active simultaneously. As a non-limiting example,in a given DBF some of the RFIOs can be in Rx mode when one of them isin Tx mode or when the mTx is also active (which would indicate that thedevice is trying to calibrate its functional Rx array).

The goal in the system design is to make mutual coupling measurementsbetween different antennas. With some paths in Rx mode and some paths inTx mode, measurement loops can be formed inside the enclosed antennasystem itself and compared to pre-stored mutual coupling levels of thecalibrated array. Any difference between the measured mutual couplingvalues during operation and the values stored in memory will beinterpreted as error and will be compensated by modifying thephase/amplitude of each RFIO path accordingly. Such error may be theresult of changing properties of the FEM, DBF, or PCB, for example, dueto temperature, aging, etc.

Stack Patch Antenna Assembly

Referring to FIGS. 3A-3B, 5A-5E, and 6A-6E, the antenna stack assembly300 will now be described in greater detail. In the illustratedembodiment, the antenna array is a stack patch antenna assembly designedto meet various goals of antenna performance, heat transfer, andmanufacturability. A patch antenna is generally a low profile antennathat can be mounted on a flat surface, including a first flat sheet (or“first patch”) of metal mounted over, but spaced from, a second flatsheet (or “second patch”) of metal, the second patch defining a groundplane. The two metal patches together form a resonant structure.

FIGS. 5A-5E illustrate top views of exemplary layers in an exemplaryantenna stack 300 seen in FIG. 3A, including a radome 305, radome spacer310 (FIGS. 5B and 5C), upper patch layer 330 (FIG. 5A), antenna spacer335 (FIG. 5D), and lower patch layer 332 (FIG. 5E).

Referring to FIGS. 6A-6D in a close-up view of individual antennaelements 313, 314, the patch antenna assembly 334 includes upper andlower antenna patches 330 a and 332 a spaced from each other to achievethe desired tuning of the patch antenna assembly 334. The individualelements 313, 314 shown in FIGS. 6A-6C are part of a plurality ofantenna elements forming an array of antenna elements (see FIG. 5A).

As seen in FIGS. 6A and 6B, the individual lower patch layer elements332 a are configured to align with the individual upper patch antennaelements 330 a, for example, in a vertical stack. The lower patchantenna elements 332 a may be the same as or similar in shape andconfiguration as the upper patch antenna elements 330 a. In theillustrated embodiment, the upper patch elements 330 a are generallycircular in configuration and include a plurality of slots for antennapolarization or tuning effects. The lower patch antenna elements 332 aare generally circular in configuration.

As seen in FIGS. 6A and 6B the upper patch antenna layer 330 is spacedfrom the lower patch antenna layer 332 using an antenna spacer 335 (notshown in FIGS. 6A and 6B, but see FIGS. 6C and 6D). Each of theplurality of apertures in the antenna spacer 335 may include a verticalpathway to align with each lower patch element 332 a (at the bottom) andeach upper patch antenna element 330 a (at the top) to define aplurality of individual antenna elements 313, 314 in the antenna lattice312.

As seen in FIG. 6C, each of the plurality of antenna elements 313, 314align with each of the plurality of apertures 317 of the cells 316 ofthe antenna spacer 310. For example, each of the antenna elements 313,314 are disposed within the cells 316 to provide suitable spacing aroundeach of the antenna elements 313, 314.

The upper antenna patch layer 330 and the lower patch antenna layer 332may be formed on standard PCB layers or other suitable substrates, suchas a thin substrate like FR4 or mylar. In one embodiment, the upper andlower patch antenna layers 330 and 332 are PCB substrates having arespective plurality of antenna patch elements 330 a and 332 a. Thefeatures of the upper and lower patch antenna layers 330 and 332 may beformed by suitable semiconductor processing to obtain the desiredfeature patterns and shapes. In the illustrated embodiment, the lowerpatch antenna layer 332 includes a grid 333 of conductive materialbetween lower patch antenna elements 332 a to create an anisotropicdielectric layer, described in greater detail below. In an alternateembodiment, the patches may be printed, for example, using a conductiveink, on the patch layers.

An array of multiple patch antennas on the same substrate can be used tomake a phased array antenna for which the antenna beam can beelectronically steered.

In some embodiments of the present disclosure, the upper and lower patchantenna elements 330 a and 332 a may have a longest dimension in therange of 6 mm to 8 mm. The center of each of the upper and lower patchantenna elements may be spaced from the center of adjacent upper andlower patch antenna elements 330 a and 332 a by a distance in the rangeof 11 mm to 13.5 mm. The cell height of the antenna spacer 335 may be inthe range of 1 mm to 2 mm. Likewise, the cell walls of the antennaspacer 335 are in the range of 1 mm to 2 mm wide. The adhesive patternsat either end of the cell walls may have a height in the range of 0.005mm to 0.01 mm.

A suitable antenna spacer 335 may be thermally conductive and capable ofdissipating heat through its structure, while also have a low dielectricconstant. In one embodiment of the present disclosure, the antennaspacer 335 may be made from plastic material, and may have a dielectricconstant, for example, of less than 3.0, less than 2.0, or less than 1.5at room temperature, and for heat dissipation, a thermal conductivityvalue of greater than 0.35 W/m-K or greater than 0.45 W/m-K. As seen inFIG. 6C, the antenna spacer 335 may have a cell and wall structure, suchas a honeycomb structure. Although illustrated and described as a singlespacing layer, the antenna spacer 335 may be comprised of a plurality ofspacer elements defining the space between the upper and lower patchlayers 330 and 332 of the patch antenna assembly 334. In anotherembodiment, the antenna spacer 335 may be a foam spacer to provideinsulative properties.

The radome portion 206 is a structural surface or enclosure thatprotects the antenna stack assembly 300, providing an environmentalbarrier and impact resistance. The radome portion 206 includes radome305 to the radome spacer 310. Radome spacer 310 may have similardimensions, properties, and adhesive properties as the antenna spacer335. However, the radome spacer 310 may have a different height than theantenna spacer 335 to provide a suitable environmental barrier, forexample, in the range of 2 mm to 3 mm.

As one non-limiting example, the lower patch antenna element is 6.8 mmin diameter, and the upper patch antenna is 7.5 mm in diameter. In theillustrated embodiment, adjacent antenna elements may be spaced 12.3 mmfrom each other, for example, in a triangular lattice. The height ofantenna spacer 335 may be 1.2 mm with a 0.075 adhesive bond line oneither side, for a total height of 1.35 mm. (The radome spacer 310 is2.35 mm thick with a 0.075 adhesive bond line on either side, for atotal thickness of 2.5 mm.) The cell walls of the antenna spacer 335 andthe radome spacer 310 are 1.5 mm with a 5 degree draft.

As can be seen in FIG. 6D, the patch antenna assembly 334 may beseparate from but mechanically and electrically supported by a printedcircuit board (PCB) assembly 342. The PCB assembly 342 is generallyconfigured to connect electronic components using conductive tracks,pads and other features etched from one or more sheet layers of copperlaminated onto and/or between sheet layers of a non-conductivesubstrate. The PCB assembly 342 may be a single or multilayer assemblywith various layers copper, laminate, substrates and may have variouscircuits formed therein. In FIG. 6A, the top layer 382 of the PCBassembly 342 is shown including the slot feed 350.

A dielectric layer 340 provides an electrical insulator between thepatch antenna assembly 334 and the PCB assembly 342. The dielectricspacer 340 may have a low dielectric constant (which may be referred toas relative permittivity), for instance in the range of about 1 to about3, or about 2 to about 3 at room temperature. (When the dielectricconstant is high, for example, higher than 3, it may create a scan angleproblem for the phased array antenna.)

In an alternate embodiment, a continuous layer dielectric spacer may bereplaced with an array of discrete spacers, such as puck spacers. Thepuck spacers may be positions under the individual stacked patch antennaelements. Puck spacers have overall less material than a continuouslayer dielectric spacer, resulting in less overall dielectric loadingand allowing for a larger scan angle. Puck spacers may be formed fromsuitable materials, such as plastic, to provide a suitable dielectricconstant and low loss tangent to conform with the performance of thepatch antenna assembly. As one non-limiting example, the puck spacersmay be formed from a polycarbonate plastic.

In typical PCB construction, individual PCB layers are typically made upof fiberglass material surrounding a pattern of copper traces definingelectrical connections. The copper and fiberglass having similar CTEvalues and generally have no purposeful air gaps within the structure.Therefore, the various layers defining a multi-layer PCB can belaminated together under high heat and pressure conditions. In typicalpatch antenna assemblies, the upper patch layer, the lower patch layer,and the spacing therebetween may be formed using a conventional PCBlamination process.

As described above, materials used in the spacing components (e.g., theradome spacer 310 and the antenna spacer 335) of the antenna stackassembly 300 may include plastic materials. Suitable adhesives inaccordance with embodiments of the present disclosure are capable ofbonding to plastics and may have a dielectric constant of less than 3.0and a thermal conductivity in the range of 0.1 to 0.5 W/m-K. Referringto FIG. 3B, the adhesive layer stack 390, which is a stack of layers inthe stack assembly 300 having adhesive 325 therebetween, including thefollowing structural layers: radome 305, radome spacer 310, upper patchantenna layer 330, antenna spacer 335, lower patch antenna layer 332,and dielectric spacer 340. In addition to the adhesive layer stack 390,in some embodiments, the PCB assembly may also be adhered by adhesivebonding and pressed with the adhesive layer stack 390 as shown by arrow398 in FIGS. 3A and 3B.

Referring to FIGS. 6A-6E, each antenna element 313 illustrated herein isan implementation of a dual polarized slot-coupled stacked patchantenna. A conductive layer 355 in PCB assembly 342 serves as theantenna ground, with a slot feed 350 (including two orthogonallyoriented slots 352 and 354) cut out in the layer 355. The slots 352 and354 are disposed under two conductive patches 330 a and 332 a stacked ontop of each other with a controlled spacing between the upper and lowerpatches and the lower patch and the slots (see FIG. 6A).

The slots 352 and 354 have feed lines 356, 358 (see FIGS. 7B and 7C)aligned with the slots 350 to create an electric field across the slots352 and 354. The induced electric field couples to the lower patch 330 ato excite the stacked patch antenna pair 330 a and 332 a. To remove backradiation, another conductive layer 361 backs the slots with enoughdistance (so that slots are not short-circuited) below the feed-lines356, 358 and slots 352 and 354 (see FIG. 6E). The second conductivelayer should be spaced far enough from the feed lines 356, 358 such thatthe feed lines 356, 358 primarily use the first conductive layer (havingthe slots) as the ground plane, without being perturbed by the presenceof the backing conductor layer.

Typically, this type of antenna is capable of achieving impedancebandwidths in excess of 50%. To achieve such performance, some of thedesign guidelines are as follows: using a low dielectric constant (lessthan 3 or in the range of about 2 to about 3) for the dielectric spacer340 disposed between the slots 350 and the lower patch 332 a and even alower dielectric constant (air gap or foam-like material) for theantenna spacer 335 disposed between the lower patch 332 a and the upperpatch 330 a. Other low dielectric materials can be used as the radomelayer 305 and/or radome spacer 310, which may function as impedancetuning superstrates.

Another performance metric of a phased array antenna designed inaccordance with embodiments of the present disclosure is the maximumangular range possible for beam-steering without any blindangle/direction. This metric typically means as little dielectricloading over the ground plane as possible to avoid trapping theelectromagnetic signals (to be radiated) along the array surface (hencecreating well-known “surface waves,” which do not leave the antennaaperture 402). Low dielectric loading can be achieved by low dielectricconstants and low thicknesses of the antenna spacer 335 and the radomespacer 310.

Environmental factors also play a role in determining the antenna stackassembly 300. The resonating antenna elements 330 a and 332 a should bekept away from the effects of rain drops or other particles potentiallysitting or moving across the antenna aperture 402, indicating that theradome 206 cannot be arbitrarily thin: it provides enough offset betweenthe environmental boundary and the upper patch 330 a so that theelectromagnetic behavior is not disturbed.

Heat generated by the active electronic components can generally bedissipated from every face of the enclosed unit, including the antennaaperture 402. The dielectric and spacer layers in the antenna stackassembly 300 can be designed for thermal conductivity using thermallyconductive plastics in the spacing elements 310 and 335 having lowthickness for optimized thru-plane heat dissipation through the radome206.

FIG. 6A-6B shows the dual slots 352, 354 on the ground plane 355 withthe stacked patch pair 330 a and 332 a on top of the slots. As seen inFIG. 6B, on the lower patch layer 330 a, a conductive grid 333 isprovided. The spacing between the grid portions can be adjusted tocontrol and/or miniaturize the size of the lower patch. The grid 333 canalso be used increase the coupling from slots to the lower patch byproviding anisotropic dielectric loading in addition to that provided bythe dielectric spacer 340, with negligible contribution to surface waveissue. (The horizontally printed square patches are almost invisible tothe first TM mode along the ground plane).

The antenna stack up (as seen in FIG. 6D) is designed with a low averagedielectric constant, improving the bandwidth and maximum achievable scanangle (for the same lateral spacing between antenna elements). Toachieve a low average dielectric constant, the dielectric spacer 340implemented may be a continuous plastic sheet of low dielectric constant(for example, 2.4). The stacked patch layers 330 and 332 can be printedon a very thin substrate, such as a thin PCB layer or a foam or otherthin plastic layer. The antenna and radome spacers 310 and 335 can beimplemented using low dielectric constant plastics (e.g. LDPE). Inaddition, using a honeycomb structure for these spacers (approximately40% or less density), the average dielectric constant is reduced evenfurther.

FIG. 6C shows a top view of the aperture without the radome 305,illustrating the location of the antenna elements relative to thehoneycomb cell walls 316. The diameter of the antenna elements can beadjusted (for example, by miniaturizing edge-slots for top patch 330 andby using a surrounding grid for the bottom patch 332) to leave spacingsurrounding around each antenna element from the honeycomb cell walls316 so that the cavity between the two patches 330 and 332 fills withair and not with dielectric material.

The spacer plastics are selected to provide thermal conductivity forheat transfer away from the active electronics.

The slots, the feed-lines of the slots and the cavity backing the slotsare implemented in PCB technology, because these components have finefeatures and vertical conductors (e.g. via) in addition to the planarconductive layers. The patch antennas and the dielectric spacers betweenthose are implemented using lower cost materials (LDPE or HDPE plastic,mylar, etc.).

Main PCB Assembly

As discussed above with reference to FIGS. 6A-6D, the PCB assembly 342includes features that may be aligned with the upper and lower antennapatch elements 330 a and 332 a of the individual antenna elements 313,314, which together may form a resonant antenna structure. As discussedabove, PCB assembly 342 includes some of the features of the antennaelements like dual slots 352 and 354 etched on the ground plane 355 withfeed lines 356, 358, a cavity 360, and a backing ground plane 361. FIG.6E illustrates a simplified sketch of the main PCB assembly 342 stack-upshowing the RF path (inside the PCB assembly) from the DBF 407 throughthe FEM 415 and up to the slot feed 350 (etched on the first metal layerof the PCB assembly 342). Because of the cross-sectional nature of thedrawing, FIG. 6E does not fully illustrate the dual slot configurationfor the slot feed 350 (slots 352 and 354), as seen in FIG. 7A, or the90-deg hybrid coupler seen in FIG. 7B.

As a non-limiting example, twelve PCB metal layers (L1 through L12) areshown in the illustrated PCB assembly 342. As discussed above, the slots352 and 354 are etched in the first metal layer (L1), the feed-lines 356and 358 (Tx and Rx routing and the 90-deg hybrid) are on the secondlayer (L2), and the secondary ground plane 355 backing the slots 352 and354 is on the fifth metal layer (L5).

To prevent the RF signals from bleeding inside PCB layers L1 to L5, theslots 352 and 354 are surrounded by grounding vias 370, 380, forming acavity 360 together with the L1 and L5 ground planes 355 and 361. Thevias guarding 370 and 380 the cavity 360 are formed by staggered laservias extending from L3 and L5 (see FIG. 6E and FIGS. 7A-7C). In anotherembodiment, the laser vias could be replaced with mechanical throughvias (from layer L1 to L12). Inside the cavity 360, metal layers L3 andL4 are etched off (see FIG. 6E and FIG. 7C). Outside the cavity 360,metal layer L3 is used as another ground plane, separating the routinglayers L2 and L4.

A plurality of cavities 360 are disposed in the PCB assembly 342, tocorrespond with the lattice 312 of the antenna elements 313 (see FIG.8A). The distances between adjacent cavities 360 and antenna elements313 is determined based on the effective dielectric constant of theantenna stack and the resulting onset frequency/scan-angle of thesurface waves and/or grating lobes. However, the effective dielectricconstant inside the main PCB assembly 342 is larger (typically >3.5)than the antenna stack 390 (see FIG. 3B), which is primarily made fromplastic and air). This difference in effective dielectric constant maycause destructive resonant modes at lower frequencies and reduce theoperational bandwidth of the antenna array at the higher end of thespectrum. Such reduction in operational bandwidth can be mitigated bydisposing random ground vias (for example, extending from L1 to L5)between the cavities and the feed lines to reduce the maximum spacingbelow a desired limit (see FIG. 8A-8B). Another suitable approach isplacing a low number of ground vias 375 (e.g., one per antenna)strategically between the cavities to reduce the average size of thegaps between cavities and move resonance frequencies higher (freeing-upthe antenna spectrum). Yet another suitable approach is placing the TXand/or RX transition vias 377 (see FIG. 8B) in strategic locations touse the ground vias of those transitions as the resonant suppressingfeatures.

The cavity 360 is designed with L5 as the backing ground plane 361 is toprovide spacing between the backing ground and the L1 slots and the L2feedlines. Closer implementation (for example, using L3 as the backingground plane and reducing the layers of the antenna cavity) might bepossible but will be more sensitive to material properties anddielectric and laminate thicknesses. In view of the L1 and L5 spacingbetween the ground plane 355 and the backing ground plane 361, L2 and L4are used as dual purpose layers. L4 is used for routing calibrationtraces and couplers (see FIGS. 4A, 6E, and 8C-8E) and low frequencydigital signals between modem, FEM 407, and DBF 415. L2 is used for90-deg hybrid coupler 462 and the Tx/Rx antenna mapping (as can be seenin FIG. 8A) for length matching purposes (if FEMs 415 are notdistributed uniformly from their respective antenna elements 413 as aresult of layout complexity on the bottom layer of the PCB assembly342). Therefore, the advantageous effect of creating a cavity 360 inL1-L5, is that the number of layers in the overall PCB assembly 342 canbe reduced resulting in optimized PCB assembly design. In that regard,other components may be disposed on the same or a nearby layer withoutinterfering with the feed structure.

Another suitable implementation would be using L3 as backing groundplane for the slots 352 and 354 but making the distance between L2 andL3 larger (for example, greater than 0.3 mm) as compared to the distancebetween L1 and L2 (for example, approximately 0.1 mm). However, suchdistancing would also be implemented in L10, L11, L12 for top/downsymmetry in the PCB assembly 342. Such spacing of L10, L11, and L12 mayaffect ground plane stitching between L10, L11, and L12, which coulddegrade the quality of the RF-breakout of the electronics (DBF, FEM,etc.).

Referring now to FIGS. 7A-7C and 8A-8E (showing the progression of L1,L2, L3, L4, and L5 in the PCB assembly 342 from the bottom view in FIGS.7A-7C and the top view in FIG. 8A-8E), the PCB assembly 342 will now bedescribed in greater detail. Referring to FIGS. 7A-7C, the slot feed 350(including slots 352 and 354) interfaces with the feed structure 364(including first and second feed lines 356 and 358) disposed in thelayers of the PCB assembly 342. The feed lines 356 and 358 couple eachantenna element 313 of an antenna lattice 312 with a specific DBF 407 inthe DBF lattice 406 (not shown in the PCB assembly layers L1-L3 in FIGS.7A-7C, but see FIG. 6E). The DBF lattice 406 (and respective FEMs 415)may be disposed in the PCB assembly 342 at a lower layer, such as abottom layer of the PCB assembly 342.

Referring to FIG. 7A, a slot feed 350 including a pair of first andsecond slots 352 and 354 is shown. In the illustrated embodiment, thefirst and second slots 352 and 354 are oriented substantially normal toone another and coupled to feed lines 356 and 358 of a 90-degree hybridcoupler 362.

As described above, each antenna element 313, 314 of the antenna lattice312 is dual circularly polarized with separate receiving Rx (e.g.,right-hand circularized ports) and transmitting Tx (e.g., left-handcircularized ports) port for each unit cell. The 90-degree hybridcoupler 362 works in conjunction with dual linearly polarized antennaelements to create circularly polarized (CP) ports for coupling with theFEM 415 and the DBF 407.

As described above, from the bottom surface of L1 extends a plurality ofground vias (e.g., metal vias or stitching) 370 defining at least aportion of cavity 360 to mitigate RF “bleeding” from the cavity 360. Thecavity 360 provides a resonant structure and enables isolation for thefeed structure 364, such that other components may be placed on thefield 368 of the same or a nearby layer without interfering with thefeed structure. Ground vias 374 also help isolate the first and secondslots 352 and 354 and feed lines 356 and 358 from each other.

Referring to FIG. 7B, L2 includes the first and second feed lines 356and 358 to interface with the slot feed 350 and the 90-degree hybridcoupler 362. In the Tx direction, the 90-degree hybrid coupler 362excites the slot feed 350 and the antenna stack (not shown). In the Rxdirection, the slot feed 350 excites the 90-degree hybrid coupler 362.As described above, in addition to the Rx and Tx lines, L2 may furtherinclude meander routing for line length consistency (not shown in FIG.7B, but see FIG. 8A).

Referring to FIG. 7C, L3 is a partial ground layer that includes acut-out portion 378 corresponding with the cavity 360 defined by theground vias 370 extending from L1. Extending from the bottom surface ofL3 are additional ground vias 380 aligned with ground vias 370 tofurther define the cavity 360.

As seen in FIG. 7C, the first and second slots 352 and 354 of the slotfeed 350 couple with the first and second feed lines 356 and 358 of the90-degree hybrid coupler 362 (with the feed lines residing in the cavity360, but the 90-degree hybrid coupler 362 outside the cavity 360), withthe first and second slots 352 and 354 and corresponding feed lines 356and 358. In the illustrated embodiment, L4 (not shown) may be a mostlyempty layer, for example, used for calibration meander termination andconnector routing for factory calibration. As seen in FIG. 6E, L5 is abacking ground plane 361 defining the cavity 360.

Referring to FIGS. 8A and 8B, the various electronic components in L1-L5are shown with the layers separating the components removed. FIG. 8B isa close up of one feed structure 364 in FIG. 8A. Referring to FIG. 8A,adjacent feed structures 364 are shown with spacing for meanderinglines. Referring to FIG. 8B, a received Rx signal from the slot feed 350and 90-degree hybrid coupler 362 travels through line 392 to the Rx DBFrouting 372 (to Rx DBF 426, see FIG. 4B). Likewise, a transmitted Txsignal from the Tx DBF 371 (from Tx DBF 425, see FIG. 4B) travelsthrough line 391 to the 90-degree hybrid coupler 360 to the slot feed350.

In the illustrated embodiment, the 3 dB 90-degree hybrid coupler 462 isimplemented as a single stage branch-line coupler (see FIG. 7B and FIG.8B). The Tx and Rx ports might have different impedance tuning featuresat the FEM chip 415 Tx and Rx pins for different frequency bands (as anon-limiting example, Tx using 14 GHz, Rx using 12 GHz). Otherimplementations of 90-degree couplers are also possible for this antennadesign (e.g. multi-stage branch-line couplers, multi-stage broadside, oredge-coupled hybrids, etc.).

Referring to FIGS. 8C-8E, an exemplary configuration for a coupler 462for calibration is provided. This particular coupler 481 is implementedalong the Rx routing (L2) between the FEM and the 90-degree hybridcoupler 462. The coupled line is disposed on L3 (FIG. 8D) with a narrowcut on the L3 ground plane and the routing back to the mTx port 431 andthe RF matched load termination 485 is disposed on L4 (FIG. 8E). Inanother embodiment, the coupled line section may be disposed on L4, butwith a lower coupling ratio.

When the calibration coupler is implemented between the antenna and FEM,the coupler is visible by the antenna and it can therefore modify theload impedance presented (by the FEM) to the antenna. This in turn mightdisturb the periodic nature of the antenna array (some elements havecouplers, others not) and cause increased side-lobe levels.

To remove the periodicity issue, the coupler features of FIGS. 8C-8E canbe implemented on every antenna and in most of the cases, the routing onL4 can be terminated with a matched load at both ends (rather than goingto mTx or mRx), leaving only a few antennas with physical connection tothe mTx/mRx ports. Even though every antenna would have same impedancein the mentioned approach, power is drawn from every antenna and FEM,whether we are routing those to mTx/mRx ports and making use of them ornot. Such approach would in turn reduce the antenna efficiency for theTx array and noise figure and G/T for the Rx array (depending on whichport we place the coupler between the 90-deg hybrid and FEM).

Instead, one could add all the features on FIGS. 8C-8E to every antennato make sure the impedance discontinuities due to the cuts along L3ground plane is common between antennas. However, include routing (onL4) traces in only a few cases, rather than all. This configurationwould in turn reduce the impact on antenna efficiency while mostly(albeit not completely) preserving the impedance consistency. Forexample, if the coupler shown in FIG. 8C-8E is a −10 dB coupler(approximately 0.45 dB or 10% power loss) and with L4 routing on oneantenna in every DBF block (of 16 antenna), the average efficiency lossper antenna in the 16-element block would be approximately 0.6%, whichis reasonable trade-off.

Algorithm for Over-the-Air Calibration

As illustrated in FIG. 4A, two signal path configurations arecontemplated for the calibration signals to follow. The DBF either might(1) be capable of sending and receiving the calibration signals throughthe functional RFIO paths (e.g., 457) or it might (2) have dedicatedpaths and pins (mTx and mRx) to transmit and receive calibration signals(e.g., 465, 467).

Regarding calibration through the RFIO path, in this mode of operation,every antenna element can be used as calibration antenna (in addition toan antenna's normal operation for communication). As illustrated in FIG.9C, to calibrate the Rx array of DBF chips 607 and 608, one of the RFIOpaths (e.g., for antenna 613 a) in DBF chip 607 might be in Tx modeoutputting a CDMA-based calibration signal through the FEM 636 (thatshould also be in Tx mode with power amplifier PA 623 amplifying thesignal). This outputted signal S3 might be received by nearby antennaelements, of which the FEM (LNA 624) and the RFIO paths are in Rx mode(to listen to the calibration signals). Such operation would allow thesame calibration signal to be received by multiple Rx paths by antennaelements 613 in DBF chip 607 and antenna elements 614 in DBF chip 608 tocreate a set of (relative) mutual coupling data/measurements amongmultiple antennas. This set of data can be compared to the pre-existingmutual coupling data (acquired in factory) expected from afully-calibrated Rx array. Any difference in magnitude/phase of themeasured data might be interpreted as error happened in field (forexample, due to aging or change of temperature) and correctedaccordingly to match to the expected mutual coupling data.

Calibrating the Tx array with a similar method is illustrated in FIG.9F, with the calibration RFIO to FEM to antenna path 613 a being in Rxmode (LNA 624), receiving signal S6, and the nearby antenna elements 613and 614 in Tx mode (PA 623) and under normal operation.

Such operation would allow multiple Tx signals from multiple nearbyantenna elements to be received by the calibration receiver MRx path byantenna element 613 a in DBF chip 607 to create a set of (relative)mutual coupling data/measurements among multiple antennas. This set ofdata can be compared to the pre-existing mutual coupling data (acquiredin factory) expected from a fully-calibrated Tx array. Any difference inmagnitude/phase of the measured data might be interpreted as errorhappened in field (for example, due to aging or change of temperature)and corrected accordingly to match to the expected mutual coupling data.

Using solely RFIO paths to transmit and receive during calibration haschallenges. One challenge is the dynamic range on the functional Rxpaths (FEM-LNA and RF Rx portions of DBFs) and/or large tuning range onthe functional Tx paths (FEM-PA and/or RF Tx portions of DBFs). Thenormal operation of the user terminal phased array has sensitive receivepaths to be able to sense low power satellite signals, and relativelyhigher power transmit signals to be able to reach the satellites. With ameasurement loop between those Tx and Rx paths on the same user terminal(to collect internal mutual coupling data) the Tx paths might easilyoverpower and saturate the sensitive Rx paths.

To avoid this saturation, the Tx paths (in Tx portions of DBF or insidethe FEM-PA) can be configured to be capable of reducing the RF gain(along that path) to a much lower value (compared to normal operation)during calibration so that the outputted calibration signals (going tothe neighbor antennas) are low-enough power (for Rx paths to be notsaturated).

Similarly, to calibrate the Tx array, the Rx paths should have enough(most probably tunable) dynamic range such that they can both receivethe satellite signals and the normal higher power Tx signals duringcalibration without corrupting the data due to saturation. Because thesecalibration modes on the RFIO paths demand unnecessary (compared to thenormal mode of operation) ranges of operation on all of these RF paths,in some cases it may be more feasible to create one dedicated Rx and onededicated Tx path per DBF (with much larger dynamic range andtune-ability) to be used for calibration (hence mRx and mTx dedicatedreceive and transmit paths).

Calibration through mTx 631 or mRx 632 involves dedicated receive andtransmit paths for the calibration signals to be transmitted orreceived. These dedicated paths can be designed and/or tuned with theexpected mutual coupling (between antennas) values in mind. Therefore,the dedicated paths may be more suitable to handle the expected signalpower levels during the calibration mode.

In some embodiments, the mRx and mTx ports may be connected to dedicatedantennas for mutual coupling measurements. These dedicated antennas canbe selected from one of the regular antennas (from the main antennalattice) to be used by those ports or might be a separate antenna placedbetween the regular antennas in the lattice. However, both of theseoptions will have degrading impact on the side lobe performance of theantenna array because, in either case, the periodicity of the lattice isbeing disturbed.

Referring to FIGS. 9A-9F, different designs for over-the air calibrationof antenna elements are provided. Referring to FIGS. 9A-9C, threeapproaches for Tx array calibration are provided. Referring to FIGS.9D-9F, three approaches for Rx array calibration are provided. In theexamples of FIGS. 9A-9C for Tx array calibration, the calibrationantenna 613 a of the DBF 607 on the left is sending a calibration signal(S1, S2, or S3) to be received by the DBF 608 on the right forcalibration of DBF 608 on the right or by the other functioning antennasin the DBF 607 on the left. In the examples of FIGS. 9D-9F, thecalibration antenna 613 a of the DBF 607 on the left is receiving acalibration signal (S4, S5, or S6) from the DBF 608 on the right or fromthe other functioning antennas in the DBF 607 on the left forcalibration of DBF 607 on the left.

As seen in FIG. 9A, the mRx 632 and mTx 631 pins of the DBF 607 can berouted to couple at coupler 679 to the normal RF paths along the RFIOrouting between DBF and FEM (for example, see coupler 479 in FIG. 4A).In another configuration as seen in FIG. 9B, the Tx/Rx antenna can berouted to couple at coupler 681 to the normal RF paths along the RFIOrouting between the 90-deg hybrid coupler and FEM (for example, seecoupler 481 in FIG. 4A).

The coupler 481 can be a 90-degree hybrid coupler with 4 ports; one formTx (or mRx), two for antenna and FEM sides and one for matchedtermination. An example of a 90-degree hybrid coupler 481 between theFEM and the 90-degree hybrid coupler is shown in FIG. 8C-8E. The couplercan be chosen to be directional or non-directional, to be able toconnect mTx or mRx from both sides of the routing and use the samecoupler by two DBFs (in this case, matched load is replaced with anothermTx or mRx of a different DBF chip).

In another embodiment of the present disclosure, a non-90-degree hybridcoupler can also be implemented inside the antenna cavity (not-shown infigures), by routing the calibration lines in and out of the antennacavity. With a controlled distance and orientation to the slots, asuitable coupler with desired coupling levels can be implemented.

In the case of calibrating the Rx array with mTx coupler between FEM andantenna, FIG. 9B illustrates the modes of operation for the DBFs andFEMs and the signal flow along different paths. All of the FEMs and theRFIO paths can be in Rx mode, while the mTx outputs the CDMA calibrationsignals from the dual-use antenna. Any neighbor antenna will belistening to the calibration signals coming from the dual usecalibration antenna 613 a. The mTx section of DBF is responsible toadjust the power levels while measuring different neighbor antennas,which might have very different coupling levels to the dual-usecalibration antenna. The coupling level of the mTx coupler can also bedesigned to make sure the mean power level is at the right value, eventhough the dynamic adjustment has to be done inside the mTx section ofDBFs.

In the case of calibrating the Rx array with mTx coupler between FEM andDBF, FIG. 9A illustrates the modes of operation for the DBFs and FEMsand the signal flow along different paths. All the FEMs associated withthe antennas are in Rx mode, except the FEM associated with the dual usecalibration antenna 613 a, which is in Tx mode because it will outputthe mTx calibration signals. All of the RFIOs are in Rx mode, except thecalibration path, which is not relevant to this mode of operation andcan be calibrated by mTx of another DBF. Any neighbor antenna will belistening to the calibration signals coming from the dual-use antenna.The mTx section of DBF is responsible to adjust the power levels whilemeasuring different neighbor antennas, which might have very differentcoupling levels to the dual-use calibration antenna. The coupling levelof the mTx coupler can also be designed to make sure the mean powerlevel is at the right value, even though the dynamic adjustment has tobe done inside the mTx section of DBFs.

In the case of calibrating Tx array with mRx coupler between the FEM andDBF, FIG. 9D illustrates the mode of operation for DBFs and FEMs and thesignal flow along different paths. All the FEMs are in Tx mode, exceptthe one we are using for the calibration path, which is in RX mode tocollect the calibration signals coming from other antennas. Therefore,the LNA (in the FEM) handles the Tx calibration signals coming fromother antennas, without being saturated. All of the RFIOs are in Txmode, except the one being used for the calibration path, which is notrelevant to this mode of operation and will be calibrated by mRx ofanother DBF. Any neighbor antenna will be radiating calibration signals,sequentially or in parallel, depending on how many independent CDMAsignals can be created and/or processed (in the DBFs) at a time. Thecalibration signals will go through the dual-use antenna, through theLNA in FEM, the mRx coupler, and into the mRx portion (then calibrationcomputing section) of the DBF to complete the measurement and acquirethe relative mutual coupling data.

In the case of calibrating Tx array with mRx coupler between the FEM andantenna, FIG. 9E illustrates the mode of operation for DBFs and FEMs andthe signal flow along different paths. All the FEMs and the RFIOs can bein Tx mode, while the mRx listens to the calibration signal coming fromthose paths by the dual-use antenna. Because the LNA of the FEM is notpart of the mutual coupling path in this scenario, it does not need tobe capable of handling the TX calibration signals (less requirement fromFEM chip). One advantage of mRx coupling between antenna and FEM is torelax the requirements on the LNA of the FEM.

The cases described above suggests we have one coupler per mRx or mTx,indicating there will be one dual-use antenna for mRx/mTx in eachantenna group of a DBF. As a non-limiting example, this indicates onecalibration antenna in every 16 elements, assuming 16 RFIO per DBF (seeFIG. 4A). Each of those calibration antennas measures a minimum numberof antennas (for example, 16 or more) such that the groups of antennasmeasured by different calibration antennas cover the entire antennaarray with enough overlap between different groups. The overlap betweendifferent groups might be used to calibrate each group of antennasrelative to each other and make the entire antenna array coherent.

It is possible to have multiple couplers per mRx/mTx routing, connectinga single calibration port to multiple antennas. This would increase thedensity of the dual-use antennas and reduce the distance and number ofantennas to be covered by each dual-use calibration antenna. As anon-limiting example, the mRx calibration traces could be routed andcoupled to multiple RFIO lines (belonging to different DBFs) beforebeing terminated by a matched load. This would provide multiple dual-useantennas to the same mRx port during TX array calibration. The operationscheme illustrated in FIG. 9D might be slightly modified: all the FEMsand RFIOs are in TX mode except the paths that mRx couples to. Amongthose coupled paths, only one of them might have the FEM in RX modewhile the others have the FEM shut OFF. The coupled RFIO paths are notrelevant to this mRx (and can be shut OFF) and can be calibrated by mRxof another DBF. By using each coupled path sequentially, single mRx portcan either have a larger reach of aperture area and/or reduce theaperture area covered by a single dual-use antenna (hence limit thedynamic range of antenna mutual coupling magnitudes).

Referring to FIG. 9A, Rx calibration can be performed by using the DBFcalibration measurement mTx 631 and connecting it to calibration line652 for coupling at coupler 653 to the line extending between thecalibration antenna 613 a and the DBF 607. In this embodiment,calibration line 652 couples between the DBF 607 and the amplifier block636 for calibration antenna 613 a. The signal received from the mTx port631 is then transmitted by the calibration antenna 613 a.

As seen in FIG. 9A, a plurality of regular antennas 613 are coupled tothe DBF 607 by a plurality of radio frequency in/out (RFIO) pinconnections corresponding to each of the plurality of antenna elements613 and configured for receiving (Rx) communication. Although theplurality of antennas 613 are shown as being configured for only Rxcommunication, each antenna 613 may be designed for switching between Rxand Tx communication.

The calibration antenna 613 a corresponding to the DBF 607 is configuredin an opposite configuration as the other antenna elements 613. In thatregard, the FEM block 636 for the specific calibration antenna 613 a isswitched from LNA to PA for calibration mode. Such switching allows thecalibration antenna 613 a to be a nominal array element duringoperation, but then turn into a calibration antenna during calibrationmode.

The calibration antenna 613 a is configured for transmitting (Tx) asignal from the measurement calibration port mTx 631 of the DBF 607 (forexample, using calibration line 652 and a −20 dB coupler 653). Thecalibration signal S1 sent by the mTx port of DBF 607 can be sensed overthe air by the antennas 613 and 614 under test in Rx mode of DBFs 607and 608, and DBFs 607 and 608 can be aligned with respect to each otherand with respect to the signal from the mTx port 631 of DBF 607.

As discussed above, the calibration antenna 613 a may be designatedspecifically for calibration and/or may be configured for normalcommunication when not in calibration mode. Likewise, one or more of anyof the other antenna elements 613 associated with DBF block 607 may beconfigured as calibration antennas.

Referring to FIG. 9B, in another configuration, Rx calibration can beperformed by using the DBF measurement Tx (mTx) port 631 and connectingit to a calibration line 662 for CDMA coupling at coupler 663 with theline extending between the calibration antenna 613 a and the DBF 607. Inthis embodiment, calibration line 662 couples between the antenna 613 aand the amplifier block 636. The mTx port 631 bypasses the amplifierblock 636 and excites the calibration antenna 613 a directly to sendcalibration signals S2 over the air to be received by the antennas 614under test in Rx mode.

Referring to FIG. 9C, Rx calibration can be performed without using theDBF measurement Tx (mTx) port 631. If the DBF is capable of sendingcalibration signals through regular RFIO lines directly (instead ofthrough an mTx port), any antenna radio frequency path (such as the linebetween the calibration antenna 613 a and the DBF 607) can be used as acalibration antenna path to transmit calibration signals S3.

Referring to FIGS. 9D-9F, similar calibration configurations areexplained, but for a Tx calibration scenario. Referring to FIG. 9D, Txcalibration can be performed by using the DBF measurement Rx (mRx) 632.Antenna signals S4 are transmitted from antenna elements 613 of DBF 607and 614 of DBF 608. The signal S4 travels to the mRx port 632 viacalibration line 672 by CDMA coupling by coupler 673 with the lineextending between the calibration antenna 613 a and the DBF 607. In thisembodiment, the calibration line 672 couples between the DBF 607 and theamplifier block 636 for calibration antenna 613 a.

Referring to FIG. 9E, in another configuration, Tx calibration can beperformed by using the DBF measurement Rx (mRx) 632. The signal S4travels to the mRx port 632 via calibration line 682 by CDMA coupling bycoupler 683 with the line extending between the calibration antenna 613a and the DBF 607. In this embodiment, the calibration line 682 couplesbetween the calibration antenna 613 a and the amplifier block 636 forcalibration antenna 613 a.

Referring to FIG. 9F, in another configuration, Tx calibration can beperformed without using the DBF measurement Rx (mRx). If the DBF iscapable of receiving calibration signals through regular RFIO linesdirectly (instead of through an mRx port), any antenna RF path (such asthe line between the calibration antenna 613 a and the DBF 607) can beused as a calibration antenna path to receive calibration signals S6over the air by antenna 613 a under test when DBF 607 is in Tx mode.

While illustrative embodiments have been illustrated and described, itwill be appreciated that various changes can be made therein withoutdeparting from the spirit and scope of the disclosure.

1. An antenna calibration system for a phased array antenna, the antennacalibration system comprising: a beamformer lattice including at leastfirst and second beamformers, wherein each of the first and secondbeamformers corresponds to a subset of antenna cells of a plurality ofantenna cells, and wherein each of the first and second beamformersincludes a calibration section for comparing a reference signal to anon-reference signal; and a calibration antenna within the subset ofantenna cells corresponding with the first beamformer, wherein thecalibration antenna is configured to deliver a first reference signal(mTx) from the first beamformer to be received by a first operatingantenna for comparison with a first non-reference signal (Rx) in thefirst beamformer or in the second beamfomer, and/or wherein thecalibration antenna is configured to deliver a second non-referencesignal (Tx) from a second operating antenna for comparison with a secondreference signal (mRx) in the first beamformer or in the secondbeamformer.
 2. The system of claim 1, wherein the first reference signalis delivered from a calibration section (mTx) of the first beamformer.3. The system of claim 1, wherein the second non-reference signal (Tx)is received in a calibration section (mRx) of the first beamformer. 4.The system of claim 1, wherein the first reference signal is deliveredfrom an RFIO of the first beamformer.
 5. The system of claim 1, whereinthe second non-reference signal is received in an RFIO of the firstbeamformer.
 6. The system of claim 1, wherein the calibration antenna isconfigured to deliver a first reference (mTx) signal from the firstbeamformer to be received by a first operating antenna for comparisonwith a first received non-reference (Rx) signal in the first beamformerand a second operating antenna for comparison with a second receivednon-reference signal (Rx) in the second beamfomer.
 7. The system ofclaim 1, wherein the calibration antenna is configured to receive afirst non-reference (Tx) signal from a first operating antennaassociated with the first beamformer and a second non-reference (Tx)signal from a second operating antenna associated with the secondbeamformer for comparison with a first reference signal (mRx) in thefirst beamformer.
 8. The system of claim 1, wherein the calibrationantenna is configured to operate partially as a calibration antenna andpartially as an operating antenna.
 9. The system of claim 1, wherein thefirst and second operating antennas are configured for sending signals,receiving signals, or both.
 10. A method for antenna calibration,comprising: obtaining a beamformer lattice including at least first andsecond beamformers, wherein each of the first and second beamformerscorresponds to a subset of antenna cells of a plurality of antennacells, and wherein each of the first and second beamformers includes acalibration section for comparing a reference signal to a non-referencesignal; and using a calibration antenna within the subset of antennacells corresponding with the first beamformer to calibrate the subset ofantenna cells, wherein the calibration antenna is configured to delivera first reference signal (mTx) from the first beamformer to be receivedby a first operating antenna for comparison with a first non-referencesignal (Rx) in the first beamformer or in the second beamfomer, and/orwherein the calibration antenna is configured to deliver a secondnon-reference signal (Tx) from a second operating antenna for comparisonwith a second reference signal (mRx) in the first beamformer or in thesecond beamformer.
 11. The method of claim 10, wherein the firstreference signal is delivered from a calibration section (mTx) of thefirst beamformer.
 12. The method of claim 10, wherein the secondnon-reference signal (Tx) is received in a calibration section (mRx) ofthe first beamformer.
 13. The method of claim 10, wherein the firstreference signal is delivered from an RFIO of the first beamformer. 14.The method of claim 10, wherein the second non-reference signal isreceived in an RFIO of the first beamformer.
 15. The method of claim 10,wherein the calibration antenna is configured to deliver a firstreference (mTx) signal from the first beamformer to be received by afirst operating antenna for comparison with a first receivednon-reference (Rx) signal in the first beamformer and a second operatingantenna for comparison with a second received non-reference signal (Rx)in the second beamfomer.
 16. The method of claim 10, wherein thecalibration antenna is configured to receive a first non-reference (Tx)signal from a first operating antenna associated with the firstbeamformer and a second non-reference (Tx) signal from a secondoperating antenna associated with the second beamformer for comparisonwith a first reference signal (mRx) in the first beamformer.
 17. Themethod of claim 10, wherein the calibration antenna is configured tooperate partially as a calibration antenna and partially as an operatingantenna.
 18. The method of claim 10, wherein the first and secondoperating antennas are configured for sending signals, receivingsignals, or both.
 19. An antenna calibration system for a phased arrayantenna, the antenna calibration system comprising: a beamformer latticeincluding at least a first beamformer, wherein the first beamformercorresponds to a plurality of antenna cells, and wherein the firstbeamformer includes a calibration section for comparing a referencesignal to a non-reference signal; and a calibration antenna within theplurality of antenna cells corresponding with the first beamformer,wherein the calibration antenna is configured to deliver a firstreference signal (mTx) from the first beamformer to be received by afirst operating antenna for comparison with a first non-reference signal(Rx) in the first beamformer and/or wherein the calibration antenna isconfigured to deliver a second non-reference signal (Tx) from a secondoperating antenna for comparison with a second reference signal (mRx) inthe first beamformer.
 20. A method for antenna calibration, comprising:obtaining a beamformer lattice including at least a first beamformer,wherein the first beamformer corresponds to a plurality of antennacells, and wherein the first beamformer includes a calibration sectionfor comparing a reference signal to a non-reference signal; and using acalibration antenna to calibrate the plurality of antenna cellscorresponding with the first beamformer, wherein the calibration antennais configured to deliver a first reference signal (mTx) from the firstbeamformer to be received by a first operating antenna for comparisonwith a first non-reference signal (Rx) in the first beamformer and/orwherein the calibration antenna is configured to deliver a secondnon-reference signal (Tx) from a second operating antenna for comparisonwith a second reference signal (mRx) in the first beamformer.